This invention relates to a process for the preparation of easily dispersible pigments of the alpha-phase modification of metal phthalocyanine pigments, especially that of copper phthalocyanines. This process provides a simple and cost-effective method for manufacturing red-shade blue pigments having high color strength.
Crude copper phthalocyanine is usually prepared by a reaction of phthalic anhydride or a derivative thereof, urea, and a copper source, or by a reaction of phthalonitrile or a derivative thereof and a copper source in an organic solvent, optionally in the presence of a catalyst such as ammonium molybdate or titanium tetrachloride. The resultant phthalocyanine particles, however, undergo crystal growth during preparation and have a major axis of about 10 to about 200 .mu.m. Such copper phthalocyanines have little or no color value as a pigment for use in inks, coating compositions, plastics, and the like. For this reason, the crude copper phthalocyanine must be further treated to obtain a high color value.
Several methods have been described for preparing pigments having improved color value but these methods typically produce only beta-phase crystal forms or mixtures of alpha- and beta-crystal forms or require the use of special additives or solvent mixtures.
For example, U.S. Pat. Nos. 4,158,572, 4,257,951, and 5,175,282 and British Patent 1,502,884 disclose methods for preparing beta-phase copper phthalocyanine pigments.
U.S. Pat. Nos. 4,039,346 and 4,104,276 disclose the use of certain phthalocyanine derivatives as additives to inhibit the "overcrystallization" that occurs when milled phthalocyanine pigments are recrystallized in organic or aqueous organic solvents. In particular, U.S. Pat. No. 4,039,346 discloses the preparation of alpha-, beta-, or gamma-phase phthalocyanines by finishing the crude pigment in sulfuric acid containing certain aminoalkyl or amino-alkylsulfonamide derivatives of copper phthalocyanine, followed by precipitation with water. U.S. Pat. No. 4,104,276 discloses a process for preparing pigmentary copper phthalocyanine pigments by first dry milling a crude copper phthalocyanine pigment, optionally followed by acid swelling with sulfuric acid, and then stirring the milled pigment in an organic or aqueous organic medium containing aminoalkyl or aminoalkylsulfonamide derivatives of copper phthalocyanine. The method disclosed in U.S. Pat. No. 4,104,276 provides pigments in various crystal forms, typically as mixtures containing both alpha- and beta-forms.
U.S. Pat. No. 4,104,277 discloses a process for preparing copper phthalocyanine pigments in the alpha-phase, the beta-phase, or a mixture thereof by first dry milling a crude copper phthalocyanine pigment (which increases the alpha-phase relative to the beta-phase) and then mixing the milled pigment with an emulsion containing an amine, water, and a surfactant.
U.S. Pat. No. 5,279,654 discloses copper phthalocyanine compositions containing certain aminoalkyl or aminoalkylsulfonamide derivatives of copper phthalocyanine and surfactants which can be milled to obtain pigmentary material containing 10-90% by weight of the alpha-phase crystal form.
U.S. Pat. No. 4,221,606 discloses a process for preparing alpha- or beta-form copper phthalocyanine pigments by stirring the pigment in water containing certain aminoalkyl derivatives of copper phthalocyanine. An alpha-form copper phthalocyanine pigment of unspecified purity was prepared by dissolving the crude pigment in aqueous sulfuric acid, precipitating the copper phthalocyanine in water, and slurrying the precipitated pigment in water containing an aminoalkyl derivative of copper phthalocyanine.
U.S. Pat. No. 3,984,433 discloses a process for preparing purified alpha-form copper phthalocyanine pigments by dissolving the crude pigment in aqueous sulfuric acid, precipitating and isolating copper phthalocyanine sulfate, hydrolyzing the sulfate with water, isolating the copper phthalocyanine, and wet-milling the pigment in water to obtain pigmentary copper phthalocyanine pigment. U.S. Pat. No. 4,224,222 discloses a similar process for preparing purified alpha-form chlorinated copper phthalocyanine pigments (which are inherently less prone to revert to beta-form pigment; see, e,g., U.S. Pat. No. 4,313,766) in which the wet-milling step is carried out in mixtures of water and organic solvents that are miscible with water or form emulsions with water.
U.S. Pat. Nos. 5,296,033 and 5,296,034 disclose closely related processes for preparing alpha-form copper phthalocyanine pigments by wet-milling with a ball mill under certain specific stirring conditions using small-diameter grinding medium, followed by finishing and isolation steps.
U.S. Pat. No. 4,313,766 discloses the preparation of beta-phase pigment if the phthalocyanines are unsubstituted or alpha-phase pigment if the phthalocyanines are chlorine-substituted by first milling the crude pigment and then treating the milled pigment with a polar aliphatic solvent in the presence of certain aminoalkylsulfonamide derivatives of copper phthalocyanine.
British Patent 2,211,509 discloses a process for preparing alpha-phase copper phthalocyanine pigments in which an initial dry-milling step is required to "activate" crude pigment. The activated pigment is then milled in water containing a surfactant. Organic solvents are not used.
European Patent Application 422,907 discloses a process for preparing copper phthalocyanine pigments in the alpha-phase or, more generally, as a mixture containing the beta-phase by dry milling a crude copper phthalocyanine pigment in the absence of a milling aid and in the presence of certain aminoalkyl or aminoalkylsulfonamide derivatives of copper phthalocyanine.
The object of the present invention is to provide an improved process for preparing alpha-phase metal phthalocyanine pigments having excellent dispersibility, tinting strength, clearness, gloss and stability in coating compositions, printing inks, plastics, and the like. The present invention provides an economical route to products that are substantially 100% alpha-phase pigments and excellent dispersibility, brilliancy, and heat stability in plastics, inks, and paints.